Variable Frequency Drive
Over the last 40 years the cost and size of Variable frequency drive has significantly reduced and performance greatly enhanced through improvements in semiconductor switching devices, simulation and control techniques, drive topologies and control hardware and software. VFDs have three main components: AC motor, controller assembly and operator interface.
The AC motor in a Variable Frequency Drive can be single-phase or three-phase. There are also synchronous motors. Of these three, three-phase motors tend to be the most frequently used as they are the most economical. The voltage stresses imposed upon induction motors that are controlled by VDFs require that the motors serve a definite purpose inverter fed duty and meet specific standards.
The Controller has three components: the rectifier bridge converter, a direct current link, and inverter. Advances in the controller have seen great improvements in the current ratings and switch frequency of power devices. For example, the insulated gate bipolar transistor has come to be particularly popular as an inverter switching device.
The operator interface enables the operator to start and stop the motor and adjust the operating speed as necessary. Additional functions include reversing, automatic control and manual speed adjustment.
Benefits of Variable Frequency Drives
If you have an application that does not have to run at full speed then a Variable Frequency Drive can greatly reduce energy costs by controlling the motor speed to match the load requirement. This can reduce energy consumption in a business facility by as much as 70 percent, not to mention reducing production costs.
You will also see increased production due to the fact that your motor is running at an efficient speed. There will be fewer mistakes and conveyor belts will not be as frequently interrupted.
The life of your equipment will be extended and you will see less downtime due to maintenance issues. Variable Frequency Drives offer protection from issues that motors commonly face such as electrical thermal overloads, phase protection, undervoltage and overvoltage. Also, with a Variable Frequency Drive the motor will not be exposed to “instant shock” but have a smooth start which further reduces the process of wear and tear. Water hammer will also be reduced or eliminated because of smooth acceleration and de acceleration cycles. VDFs are also consume less energy than other speed control techniques when the load is below that of the usual requirement.